Cathode-ray tube having a plated inner metal layer of high-tensile strength

ABSTRACT

A cathode-ray tube in which the conductive thin film on the inner surface of the glass tube is formed of a high-tensile strength metallic-plating layer.

United States Patent Fukushima et al.

[54] CATHODE-RAY TUBE HAVING A PLATED INNER METAL LAYER OF lllGll-TENSILE STRENGTH 4 [72] inventors: Mlsakazu Fukushima, Hachioji-shi; KIIII- hiro Kimura, Tokyo, both of Japan [73] Assignee: Hitachi, Ltd., Tokyo-to, Japan [22] Filed: Sept. 30, 1968 *[2l] Appl. No.1 763,796

301 Foreign Application Priority om Oct. 23, 1967 Japan.. ..42[67854 521 05.01.... muslin/s13 51 mm. .1101; l9/40,I-i0lj 29/02 [58] FieldoiSearch ..313/s2, 107,269,252, 64,

(56] References cm 1 UNITED-STATES PATENTS Feb. I, 1972 2,232,083 2/ I941 Strohfeldt ..3 13/107 X 2,438,668 3/l948 Koch et ah... ..3l3/92 X 2,683,67l 7/1954 Findlay et al. ....3l3/l07 X 3,355,617 [1 96? Schwartz et al ..3l3/82 FOREIGN PATENTS OR APPLICATIQNS 500,589 2/1939 Great Britain "313/107 Primary Examiner-Roy Lake Assistant Examiner-V. Latranchi Attorney-Craig, Antonelli & Hill [57] ABSTRACT A cathode-ray tube in which the conductive thin film on the inner surface of the glass tube is formed of a high-tensile strength metallic-plating layer.

, 6 Drawing Figures PATENTED res 11972 FIG.

INVENTORS lfflsfiknzu FUKUJMINF ATTORNEYS CATIIODE-RAY TUBE HAVING A PLATED INNER METAL LAYER F IIIGl'I-TENSILE STRENGTH This invention relates to a cathode-ray tube, and more specifically to improvements in conductive thin films formed on the inner wall surface of a cathode-ray tube.

A cathode-ray tube must have a conductive thin film on the inner wall surface extending from the vicinity of the screen to the electron gun for the application of the anode voltage creating an accelerating field for the electron beam. Heretofore, this conductive film has been formed by a mixture of graphite powder and potassium silicate applied on the inner wall surface, and then baked to form the coated layer. For the purpose of electrical connection thereto by various electrodes in the tube, the coated film of graphite thus formed is required to be in contact with metallic springs at some points. Accordingly, the graphite coating may be scratched off by springs as an electrode is subsequently incorporated in the tube. Vibrations and impact to the tube may also cause the springs to flake off the graphite film, or the film itself may chip away from the glass at points where the strength of the bond is insufficient and fall upon the electrodes within the tube, eventually causing various troubles, such as a reduction of the breakdown voltage due to undesirable concentrations of the electric field of luminescence by virtue of stray emission at undesired parts of the viewing screen dueto the stray pieces of coating.

Attempts have been made to replace the graphite coating with a conductive film of other material, e.g., a film of aluminum formed by vacuum evaporation of a coated film of silver paste. However, these conductive materials have lowtensile strength so that, particularly when the voltage applied to the anode electrode is as high as kv. or more, as in color television receivers, the film may flake off under the action of the resulting electrostatic force and deposit on the electrode, thus causing eventually a drop in the breakdown voltage or other adverse effects of stray emission in the same manner as encountered with the graphite coating.

The object of the invention is to provide a cathode-ray tube which has improved breakdown voltage characteristics and is capable of avoiding stray emission.

In order to achieve this object, the cathode-ray tube of the invention is formedof a conductive thin film of a high tensile strength metal on the inner surface of the glass envelope. A cathode-ray tube having such a conductive film has the advantage of improved breakdown voltage characteristics and elimination of stray emission, and is useful with special advantages for color television.

These and other objects and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 1

FIG. 1 is a view showing in section the construction of a cathode-ray tube for color television embodying the present invention;

FIG. 2 is a view showing in section the construction of a cathode-ray tube for monochrome television embodying the invention; and

FIG. 3 is a view showing partly in section the construction of an electron gun in the neck of a cathode-ray tube embodying the invention.

Referring specifically to FIG. I, a glass tube is generally in dicated at 1, containing an electron gun assembly 2, a screen formed of a fluorescent layer 3 overlaid with aconductive thin film, a conductive thin film 4 formed on the inner surface of the glass tube, a shadow mask 5, and a high-voltage terminal 6 for the conductive film 4. Between the electron gun 2 and conductive film 4 there is provided a contact spring 7 for establishing an electric contact with the conductive film. Another contact spring 8 electrically connects the fluorescent layer 3 and conductive thin film 4 through shadow mask 5. To ensure a high degree of vacuum in'the tube there is provided a getter ring 9.

In the tube of the above construction, the conductive thin film is formed of a high-tensile strength material, e.g., silver,

platinum, nickel, tungsten, molybdenum, or chromium, as by electroless-plating, electroplating, or vapor-plating. Of these film-forming techniques, electroplating is directly applicable to the inner surface of glass tube I and requires an undercoating of conductive film such as "Nesa," while electroIess-plating and vapor-plating can be performed directly on the inner glass surface. 0f the high-tensile strength materials above mentioned, nickelis most preferred because it has relatively high stress, is rather inexpensive, and can easily form a plating layer.

By forming a plating layer of such high-tensile strength material, it is possible to preclude any peeling of the metallic film in flakes from the glass surface due to contact with the contact springs, vibrations of or impacts on the tube, or by the action of electrostatic force, thereby to improve the breakdown voltage characteristics and eliminate any stray emission and reduce the percentage of defective tubes to a minimum.

For example, in vibration-dropping tests, with the application of up to 100 G. (G. acceleration of gravity). 80 percent of the conventional cathode-ray tubes completed with a graphite coating were found defective in breakdown voltage characteristics while the cathode-ray tubes having a plating layer of high-tensile strength material proved totally flawless.

Further, if a graphite coating is applied on the nickel-plating layer and the two are heat-treated at a suitable temperature, a surface layer of nickel carbide will be formed over the nickelplating layer, whereby the nickel-plating layer will be blackened on the surface. This not only avoids undesirable reflection of light therefrom against the view screen, but minimizes secondary electron emission by virtue of the fact that the plating layer is coated with an overlying layer containing carbon, a substance of small atomic number. In this way the unfavorable influence of a straight nickel-plating layer can be readily overcome by the surface treatment with carbon.

In FIG. 2, showing the construction in section of a cathoderay tube for monochrome television which is another embodiment of the invention, like reference numerals have been used to designate like parts provided in FlG l. A graphite coating generally indicated at 10 is provided on the inner surface of tube 1. In this embodiment the plating layer 4 is formed only partially on the inner surface of the glass tube. Since the conductive thin film in the area of contact with the contact spring 7 is most likely to be scratched off, that area is overlaid with a plating layer 4. This partial plating can prevent to a considerable extent the degradation of breakdown voltage characteristics.

FIG. 3 shows the constniction in section of a cathode-ray tube which represents a further embodiment of the present invention. Reference numeral2 indicates an electron gun elec trically connected to a conductive thin film 4 by way of a con tact spring 7, and numeral 11 designates a lens ,gap of the electron gun 2.

-In cathode-ray tubes of certain types, the periphery of the lens gap 11 is shielded with a metal sheet. This metal sheet is employed as a shielding electrode to prevent the inner wall of a cathode-ray tube, made of a dielectric material, for example glass, from being charged up, thereby eliminating a convergence error induced in a color cathode-ray tube. The third embodiment of the present invention dispenses with this metal sheet but provides a conductive thin film 4 of a plating layer extended to the neck of the glass tube surrounding the electron gun thereby to serve as a shielding electrode. This eliminates the necessity of providing a separate shielding electrode around the electron gun and renders it easy to assemble the gun and insert the assembly into the glass tube. Moreover, because the conductive thin film is a plating layer of high-tensile strength, it can well resist the scratching effect of the contact spring at the time of insertion of the electron gun.

1. In a cathode-ray tube including a hollow envelope and at least one electrode element mounted within said envelope, an anode electrode being connected to said electrode element and comprising a conductive thin film formed on the inner surface of said envelope, at least a portion of said thin film being formed of a metallic-plated layer of high-tensile strength.

2. A cathode ray tube according to claim 1 wherein said conductive thin film is formed of a nickel plated layer and said nickel-plated layer is overlaid with a thin film 3. The combination of claim 1 wherein said one electrode element has at least one conductive spring in contact with said conductive thin film, the portion of said thin film formed by said metallic-plated layer of high-tensile strength being the 

2. A cathode ray tube according to claim 1 wherein said conductive thin film is formed of a nickel plated layer and said nickel-plated layer is overlaid with a thin film
 3. The combination of claim 1 wherein said one electrode element has at least one conductive spring in contact with said conductive thin film, the portion of said thin film formed by said metallic-plated layer of high-tensile strength being the portion connected to said one electrode element by way of said conductive spring.
 4. The combination of claim 1 wherein said one electrode element forms part of an electron-gun construction including an electron lens, and said anode covers the inner surface of said envelope surrounding said electron lens.
 5. The combination of claim 1 wherein said metallic-plated layer is made of nickel.
 6. The combination of claim 1 wherein said metallic-plated layer is made of a metal selected from the group consisting of silver, platinum, nickel, tungsten, molybdenum and chromium. 